1. Field of the Invention
The invention is directed to methods and devices for drilling well bores, specifically, the invention is directed to methods and devices for increasing the drift diameter and improving the quality of a well bore.
2. Background of the Invention
Horizontal, directional, S curve, and most vertical wells are drilled with a bit driven by a bent housing downhole mud/air motor, which can be orientated to build or drop angle and can turn right or left. The drill string is orientated to point the bent housing mud/air motor in the desired direction. This is commonly called “sliding”. Sliding forces the drill bit to navigate along the desired path, with the rest of the drill string to following.
Repeated correcting of the direction of the well bore causes micro-ledging and “doglegs,” inducing friction and drag between the well bore and the bottom hole assembly and drill string. This undesired friction causes several negatives on the drilling process, including but not limited to: increasing torque and drag, ineffective weighting on bit transfer, eccentric wearing on the drill string and BHA, increasing the number of days to drill the well, drill string failures, limiting the distance the well bore can be extended, and issues related to inserting the production string into the well bore.
When a dogleg, spiraled path, or tortuous path is cut by a drill bit, the relatively unobstructed passageway following the center of the well bore may yield a smaller diameter than the well bore itself. This relatively unobstructed passageway is sometimes referred to as the “drift” and the nominal diameter of the passageway is sometimes referred to as the “drift diameter”. The “drift” of a passageway is generally formed by well bore surfaces forming the inside radii of curves along the path of the well bore. Passage of pipe or tools through the relatively unobstructed drift of the well bore is sometimes referred to as “drift” or “drifting”.
In general, to address these difficulties the drift diameter has been enlarged with conventional reaming techniques by enlarging the diameter of the entire well bore. Such reaming has been completed as an additional step, after drilling of the well bore is completed. Doing so has been necessary to avoid unacceptable increases in torque and drag during drilling. Such additional reaming runs add considerable expense and time to completion of the well. Moreover, conventional reaming techniques frequently do not improve the well bore, but instead simply enlarge certain areas of the well bore.
Accordingly, a need exists for a reamer that reduces the torque and drag on the drill string and produces closer to drift well bore.
A need also exists for a reamer capable of enlarging the diameter of the well bore drift passageway, without needing to enlarge the diameter of the entire well bore.